There are a lot of problems that could fit in those ???. * symbolic computation (there are many Computer Algebra Systems written in Lisp like Maxima/Macsyma,

There are a lot of problems that could fit in those ???. * symbolic computation (there are many Computer Algebra Systems written in Lisp like Maxima/Macsyma, FriCAS/OpenAxiom, Reduce, bergman) * language processing * artificial intelligence * generally complex and dynamic tasks in science and engineering. Some of the software is being continually improved since the 70ties and while it doesn't have millions of people staring at it, it is useful and appreciated.